<%@ page contentType="image/jpeg" import="java.awt.*,java.awt.image.*,java.util.*,javax.imageio.*" %>
<%!
		Color getRandColor(int fc,int bc){//给定范围获得随机颜色
	        Random random = new Random();
	        if(fc>255) fc=255;
	        if(bc>255) bc=255;
	        int r=fc+random.nextInt(bc-fc);
	        int g=fc+random.nextInt(bc-fc);
	        int b=fc+random.nextInt(bc-fc);
	        return new Color(r,g,b);
	        }
%><%
	//设置页面不缓存
		response.reset();
                out.clear();
		response.setHeader("Pragma", "No-cache");
		response.setHeader("Cache-Control", "no-cache");

		response.setDateHeader("Expires", 0);
		// 在内存中创建图象
		int width = 60, height = 20;
		BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);

		// 获取图形上下文
		Graphics g = image.getGraphics();

		//生成随机类
		Random random = new Random();

		// 设定背景色
		g.setColor(getRandColor(240, 250));
		g.fillRect(0, 0, width, height);

		//设定字体
		g.setFont(new Font("", Font.BOLD, 18));

		//画边框
		//g.setColor(new Color());
		//g.drawRect(0,0,width-1,height-1);

		// 随机产生10条干扰线，使图象中的认证码不易被其它程序探测到
		g.setColor(getRandColor(150, 200));
		for (int i = 0; i < 10; i++) {
			int x = random.nextInt(width);
			int y = random.nextInt(height);
			int xl = random.nextInt(12);
			int yl = random.nextInt(12);
			g.drawLine(x, y, x + xl, y + yl);
		}

		// 取随机产生的认证码(4位数字)
		String sRand = "";
		for (int i = 0; i < 4; i++) {
			String rand = String.valueOf(random.nextInt(10));

			//rand="1";
			sRand += rand;
			// 将认证码显示到图象中
			g.setColor(new Color(20 + random.nextInt(150), 20 + random.nextInt(150), 20 + random.nextInt(150)));
			//调用函数出来的颜色相同，可能是因为种子太接近，所以只能直接生成
			g.drawString(rand, 14 * i + 6, 16);
		}

		// 将认证码存入SESSION
		session.setAttribute("checkcode_rand",sRand); 

		// 图象生效
		g.dispose();

		// 输出图象到页面
		ImageIO.write(image, "JPEG", response.getOutputStream());
%>